In many medical situations, it becomes necessary or desirable to aid the patient's blood flow. In some cases, such as certain types of open heart surgery, it is necessary for external means to completely take over the blood pumping function of the heart since the heart is incapable of doing so. In other cases, the heart is weak and external means are used to aid the heart in its blood pumping function. In still other situations, certain organs, including the heart itself, require blood flow which the body is incapable of providing and which therefore must be supplied or assisted by external means.
It has been recognized that in all situations of the type described, it is preferable to have the blood pumped in a pulsatile manner, similar to the pumping action of a normal heart. On the other hand, this pulsatile flow must be provided with as little trauma to the blood as possible, since if the blood is subjected to high shear forces, it undergoes considerable damage. Such shear forces are encountered in certain types of pumps, such as roller pumps, which pump the blood by squeezing a plastic tubing containing the blood. Also any device containing valves is likely to damage the blood through the opening and closing of the valves. Therefore, during the past several years, attempts have been made to develop a system that will circulate the blood in a pulsatile manner and will, at the same time, not subject the blood to undue trauma. Tube-pumps, piston-pumps, diaphragm-pumps, sac pumps, peristaltic or finger pumps, and roller pumps have all been tried. They have all proved inadequate -- the tube, diaphragm, piston and sac type pumps paying the price for pulsatile flow in increased blood trauma (hemolysis) caused by their valves and shear forces; the finger and roller pumps limiting operative time by the blood trauma induced by the nature of their occlusive action. The roller pump, notwithstanding its limitations, has become the standard pump used as the present day arterial perfusion pump, coronary perfusion pump, and venous and suction pump. Surgical procedure, such as cardio-pulmonary bypass, as it is understood at present, is therefore limited both in time and efficacy. The operative time is limited by the trauma induced to the blood by the occlusive pumping action and the efficacy by the lack of pulsatile flow.